Field of the Disclosure
The present disclosure relates to an electrophotographic apparatus such as a copier, a printer, or a facsimile.
Description of the Related Art
Every related-art image forming apparatus of an electrophotographic system, such as a copier, a laser beam printer, or a facsimile, is provided with a developing device. The developing device is provided with a roller-shaped developer bearing member that is disposed in such a manner that an opening of a developing container which contains mainly developer (toner) is blocked and a part of the developer bearing member is exposed. The developing device is also provided with a developer regulating member that contacts the surface of the developer bearing member to regulate the amount of developer conveyed by the developer bearing member to a constant amount. When the toner attached to the surface of the developer bearing member passes through the developer regulating member in accordance with the rotation of the developer bearing member, extra toner is removed from the surface of the developer bearing member and returned to the developer container, so that a thin layer of toner is formed on the developer bearing member. A frictional charge (also referred to as triboelectricity) is applied to the thin film of toner formed on the developer bearing member due to the friction between the developer bearing member and the developer regulating member. Japanese Patent Laid-Open No. 2005-157124 discloses a technique in which a potential difference is caused between a developer regulating member and a developer bearing member to thereby enable control of the amount of frictional charge. In a portion where the developer bearing member is exposed from the developer container, toner having a frictional charge is moved onto an electrostatic latent image formed on the surface of the photosensitive member which serves as an image bearing member that rotates in opposition to the developer bearing member.
As such a developing device, a cartridge system that is delivered to each user from a manufacturer in the form of a cartridge is generally employed. For example, when the toner contained in the developing device is depleted and printing cannot be performed, the user purchases a new developing device, which is configured to be detachably attached to an image forming apparatus, and inserts the developing device into the image forming apparatus for use. A new developing device may be shipped in a state where a containing unit that contains toner is sealed with a seal member, from the viewpoint that toner contained in the new developing device to be shipped from a manufacturer is prevented from leaking out of the developing container during transportation.
In the new developing device in which an accommodating portion is sealed, it may take a long time to supply a sufficient amount of toner contained in the containing unit to a surrounding portion of the developer bearing member. Accordingly, when the developing device is rotationally driven, in particular, the frictional resistance between the developer bearing member and the developer regulating member is extremely large. As a result, the developer regulating member may be rolled up, or a gear associated with driving of the developing device may be damaged. Accordingly, Japanese Patent Laid-Open No. H08-227212 proposes a method in which powder coating agent is applied around a developer bearing member at the time of shipment of a new developing device and the developer bearing member is caused to function as lubricant, thereby reducing a rotation torque.
As a material of lubricant applied on the developer bearing member, a material to be charged to a polarity opposite to that of toner when a thin film is formed on the developer bearing member may be used, from the viewpoint of chargeability. In Japanese Patent No. 4261941, the polarity of lubricant applied on the developer bearing member is set to be opposite to the polarity of toner, thereby preventing a reduction in image density in the usage initial stage of the developing device.
However, as discussed in Japanese Patent. Laid-Open No. 2005-157124, the image forming apparatus having a configuration in which, in an image forming mode, the potential difference obtained by subtracting the voltage applied to the developer bearing member from the voltage applied to the regulating member is set to the same polarity as that of developer has a problem. That is, in such a configuration, the use of a lubricant having a polarity opposite to that of toner may cause melt-adhesion of the lubricant to the regulating member, which may have an adverse effect on the image quality.